<!DOCTYPE html>
<html>
	<head>
		<meta charset="utf-8">
		<title>派生.子代选择器</title>
		<style>
			#header span{
				display: block;
				width: 50%;
				background-color: #00ffff;
			}
			#header>span{
				background-color: #ffaa00;
			}
			#header>span:hover{
				background-color: #00ff7f;
			}
		</style>
	</head>
	<body>
		<div id="header">
			<span>左侧导航区</span>
			<span>
				<div class="header">
			<span>右侧导航区1</span>
			<span>右侧导航区2</span>
		</div>
		</span>
		</div>
		</header>
	</body>
</html>